The US policy is to use the threat of overwhelming force, nuclear and non-nuclear, for leverage in interstate conflict whatever that conflict may be and whether or not that conflict is a threat to the United States or its persons or just the outcomes it is interested in.
It's possible that nuclear forces could be used in a scenario like you suggest, but to round that up to policy is inaccurate and it is misleading.
The US policy is to use the threat of overwhelming force, nuclear and non-nuclear, for leverage in interstate conflict whatever that conflict may be and whether or not that conflict is a threat to the United States or its persons or just the outcomes it is interested in.
It's possible that nuclear forces could be used in a scenario like you suggest, but to round that up to policy is inaccurate and it is misleading.